Photographic elements having protective overcoat layers are well known and a wide variety of different coating compositions have been proposed in the past for use as protective overcoats. Such overcoats serve a number of different purposes, such as to provide protection against fingerprints, abrasion and scratching, to protect against water spotting, to provide a particular surface texture such as a matte surface, to provide protection against blocking, and to act as anti-reflection layers which reduce glare. Layers of a temporary nature which are intended to be removed after they have served their purpose and layers which are permanently bonded to the photographic element have been described in the prior art. Protective overcoats can be applied to photographic elements by coating solutions or dispersions of film-forming agents in organic solvents such as are described, for example, in U.S. Pat. Nos. 2,259,009; 2,331,746; 2,706,686; 3,113,867; 3,190,197 and 3,415,670; by coating of aqueous film-forming compositions such as are described, for example, in U.S. Pat. Nos. 2,173,480; 2,798,004; 3,502,501 and 3,733,293; by coating of compositions containing discrete, transparent, solid particles of submicroscopic size as described in U.S. Pat. No. 2,536,764; by coating of plasticized polymer compositions as described in U.S. Pat. No. 3,443,946; by coating of polymerized perfluorinated olefins as described in U.S. Pat. No. 3,617,354; and by lamination of a protective layer as described, for example, in U.S. Pat. Nos. 3,397,980 and 3,697,277.
Many of the compositions used in the past to form protective overcoats on photographic elements have suffered from disadvantages which have greatly limited their usefulness. For example, it has been particularly difficult to formulate compositions which are fully satisfactory in providing abrasion and scratch resistance for photographic elements which are commonly subjected to severe conditions in handling and use, such as microfiche and motion picture films. Protective overcoats for such elements must meet exacting requirements with respect to factors such as transparency and flexibility as well as abrasion resistance and scratch resistance, and must be very strongly bonded to the underlying material to avoid the possibility of delamination.
An effective solution to the problem of providing useful protective overcoats for photographic elements, such as microfiche and motion picture films, which are subject to severe conditions of use, is disclosed in U.S. Pat. No. 4,092,173, "Photographic Elements Coated With Protective Overcoats," C. P. Novak, E. D. Morrison and G. M. Leszyk, issued May 30, 1978. As described in this patent, protective overcoats are formed on photographic elements by coating the element with a radiation-curable composition, comprising an acrylated urethane, an aliphatic ethylenically-unsaturated carboxylic acid and a multi-functional acrylate, and irradiating the coating to bond it to the element and cure it to form a transparent, flexible, scratch-resistant, cross-linked polymeric layer. The protective overcoat layer can be applied to the image-bearing side of the element or to the support side of the element or to both sides. As further described in U.S. Pat. No. 4,171,979 "Method Of Treating Scratched Or Abraded Photographic Elements With Radiation-Curable Compositions Comprising An Acrylated Urethane, An Aliphatic Ethylenically-Unsaturated Carboxylic Acid And A Multifunctional Acrylate," C. P. Novak, E. D. Morrison and G. M. Leszyk, issued Oct. 23, 1979, the compositions of U.S. Pat. No. 4,092,173 are also useful as restorative compositions in the treatment of photographic elements, such as still films, motion picture films, paper prints, microfiche, and the like, which have defects such as scratches, abrasion marks, and the like, which impair the appearance or projection capabilities of the element. In use as a restorative composition, the radiation-curable composition can be applied locally in the region of the defects only, to effectively eliminate them and restore the element to a substantially defect-free condition, or it can be applied over the entire surface of the element to both eliminate the defects and form a protective overcoat layer that is capable of providing protection against subsequent scratching or abrasion.
An important improvement to the radiation-curable coating composition of U.S. Pat. Nos. 4,022,173 and 4,171,979 is described in U.S. Pat. No. 4,333,998 "Radiation-Curable Composition for Restorative And/Or Protective Treatment of Photographic Elements" by G. M. Leszyk issued June 8, 1982. The improvement relates to the incorporation in the coating composition of a siloxy-containing polycarbinol, such as a polydimethylsiloxane containing alcohol functional groups grafted onto the siloxane chain, to provide improved wetting, leveling and coating characteristics, to provide improved adhesion to the photographic element, and to provide improved hardness, increased scratch resistance, and reduced coefficient of friction.
While the radiation-curable coating compositions of the aforesaid patents represent an important advance in the art of providing protective overcoats and/or restorative treatments for photographic elements, still further improvement in such compositions would be highly desirable. In particular, it would be especially advantageous to provide a coating composition which exhibits excellent adhesion toward processed photographic emulsion layers and toward all of the various types of support materials commonly used for photographic elements, for example the cellulose acetate support materials and the polyester support materials. In this way, a single formulation can be used to treat a variety of photographic products, as contrasted with the much less advantageous approach of providing a separate formulation tailored to use with each of a variety of products. Furthermore, it would be highly advantageous to provide a coating composition that does not require the presence of an aliphatic ethylenically-unsaturated carboxylic acid, since such acids can create an objectionable odor problem, can contribute to poor shelf-life characteristics, and can bring about undesirable chemical attack on some of the components of photographic elements.
It is toward the objective of providing a novel radiation-curable coating composition that provides the above improvements that the present invention is directed.